ADT will not allow creation of Android Activity
Solution 1:
If you updated to Android SDK Tools version 22.6, you are required to Update DDMS Tools and Plugins.
Go to "Help Menu Bar" -> "Install New software" and install (this will update it) url: https://dl-ssl.google.com/android/eclipse/
Also update "Developer Tools" and "NDK Plugins" to latest Version. This steps is useful for me and worked also.
Solution 2:
The comment see comment by NewShelbyWoo solved the issue